Vehicle transmission systems



Dec. 8, 1970 c. R. SCHOFIELD VEHICLE TRANSMISSION SYSTEMS 9 Sheets-Sheet1 Filed Oc t, 10, 1968 C. R. SCHOFIELD VEHICLE TRANSMISSION SYSTEMS Dec.8, 1970 9 Sheets-Sheet 2 Filed Oct. 10, 1968 Q0- QDN VOW t: ELL

N2 wt Dec. 8,1970 I c. R. scHdHE D 1- 3,545,302

VEHICLE TRANSMISSION SYSTEMS Filed Opt. 10, 1968 9 Sheets-Sheet :5

Dec. 8,1970 0. R. SCHOFIELD VEHICLE TRANSMISSION SYSTEMS I 9Sheets-Sheet 4.

Filed o t; 10, 1968 Dec. 8, 1970 (LR. S CHOFIELD 3, 2

VEHICLE TRANSMISSION SYSTEMS fQSheets-Sheet 5 Filed Oct. 10, 1968 Dec.8, I970 Filed Oct, 10, 1968 ROTATIONAL SPEEDS INRELATION To"ENGINE-SPEED c. R. SCHOFIELD VEHICLE TRANSMISSION SYSTEMS 9 Sheets-Sheet8 1ST REGIME 2ND REGIME I (LOW)\ (HIGH) o w Y4? I I-l-l I 2 (9 Q? 2----'z I 0 p LUI S g: 4o BL- E 0" 9 o d3 (9 z 035 UJ I I i m 1-0 1-5 2 z 5BRAKE DRUM BH 0 ---1 I I I F E I l I I ve a 0, FIG.& I

9 Sheets-Sheet 9 Filed Oct. 10, 1968 United States Patent U.S. Cl.74-691 5 Claims ABSTRACT OF THE DISCLOSURE This invention is concernedwith a variable-speed transmission system, especially for vehicles,including a steplessly variable unit and a planetary gear train. Bylocking one or other of two parts of the planetary gear train, tworegimes of operation can be achieved. In one regime, which is the lowgear regime for vehicles, and can also include a reverse drive, theplanetary gear train acts as a sort of differential gear. In the otherregime this differential effect is absent and the variable unit drivesthe output direct. The specification is particularly concerned witharrangements for changing over automatically from one regime ofoperation to the other.

vention is concerned with improvements in a form of transmission systemdescribed basically and in improved forms in British Pat. No. 1,078,791.

The basic transmission over which the present invention is animprovement may be defined as comprising a variable ratio transmissionunit (which will be called a variable unit) of which the drive ratio issteplessly variable and which is driven by the transmission input memberand is arranged to drive the transmission output member either via aplanetary gear train or the equivalent, in what will be termed the firstregime, or directly in what will be termed the second regime.

In this context, as in Pat. No. 1,078,791, we will refere to the driveratio of the transmission system as being high when the ratio of outputspeed to input speed is high; conversely a low ratio is one in which theratio of output speed to input speed is low.

In order to cover the transmission ratio range of the system as a whole,from one end of the range to the other, the drive ratio of the variableunit is changed firstly in one sense to substantially its limit in thatparticular sense, this being one regime of operation of the system, andis changed in the opposite sense during the other regime of operation.In other words, no abrupt change in the drive ratio of the variable unitis needed when changing from one regime of operation to the other.

This form of transmission system is referred to in Pat. No. 1,078,791 asa synchronous form, as opposed to the alternative asynchronous form alsodescribed in Pat. No. 1,078,791. The present invention is particularlyconcerned with such a synchronous form and the above synchronous form oftransmission will be referred to as a transmission system of the kinddescribed.

A main feature of this invention is concerned with an arrangement forchanging over automatically from one regime to the other. As mentionedin Pat. No. 1,078,- 791, the planetary gear train can be arranged toinclude two rotary parts each of which is locked against rotation by abrake to produce one regime of operation of the system, and is free torotate during the other regime of 'ice operation. In other words, one ofthe rotary parts is locked to produce one regime of operation, and theother is locked to produce the other regime of operation. The planetarygear train can be such that each rotary part, when it is rotating, slowsdown to a stop as the transmission ratio of the system approaches andthen reaches the point beyond which further changes in the same senserequire the other regime of operation; if the regime of operation isnotchanged then the rotary part begins to rotate in the opposite direction.Regime changing according to this invention is initiated by means of achangeover device in response to this contra-rotation of the rotarypart.

According to this invention, the normal directions of rotation of thetwo regime-controlling rotary parts of the planetary gear train areopposite. Each of these rotary parts cooperates with a regime changeoverdevice which it can drive during contra-rotation but not during rotationin its normal direction, and the two regime changeover devices areconnected to a regime control member which operates a brake to lock theappropriate rotary part of the planetary gear train (depending uponwhich direction the regime is being changed) to bring about thenecessary regime change automatically when that rotary part begins itscontra-rotation and accordingly drives the cooperating changeoverdevice.

A preferred form of changeover device including a toggle mechanism willbe described with reference to the accompanying drawings.

In the preferred arrangement for use as a vehicle transmission, the lowratios for forward drive are provided by the first regime, and thesystem can provide a zero output speed at one point. in the firstregime. The variable unit drive ratio can be changed in either sensefrom this zero output point. A change in one sense is towards the limitat which the change is reversed for the second regime of operation, anda change in the other sense produces a progressively increasing outputspeed in the reverse direction and is therefore used for driving thevehicle in reverse. Forward driving of the vehicle from start makes usefirstly of the first regime, starting from the zero output point of thevariable unit (i.e., the point in the variable unit range at Which thesystem as a whole has a zero output), and then after the vehicle hasaccelerated with a progressively increasing transmission ratio, thevariable unit eventually reaches the limiting ratio position in whichthe second regime of operation can be started to increase the overalltransmission ratio still further (that is unless, for example, thevehicle is on a hill and requires a continuously low transmissionratio). This process reversesas the Vehicle slows down and finallystops.

Examples of transmission systems according to this invention as appliedto a vehicle drive will now be described with reference tothe'accompanying drawings.

In these drawings:

FIG. 1 is a general diagrammatic view of the main mechanical parts ofthe system;

FIG. 2 is a diagrammatic view of the control circuit of t thetransmission While operating in the low regime and FIG. 7 shows apreferred changeover device for controlling the regime of operation;

FIG. 8 is a graph showing various relative speeds plotted against thetransmission ratio of the system as a whole;

FIG. 9 shows part of a modified control circuit; and

FIG. 10 shows a detail of the circuit shown in FIG. 9

As shown in FIG. 1, the transmission system has an input shaft 2 whichserves'as the input to a variable ratio frictional drive unit 4 and alsoextends from the far end of the variable unit 4 and into a planetarygear train 6. The shaft 2 is driven by an engine shaft 7 via anepicyclic gear 5 having a 3:2 step-up drive ratio; the gear 5 comprisesplanetary gears 11 which are carried by the shaft 7 and which meshinternally and externally respectively with a stationary gear member 13and an annular gear 15 connected to the shaft 2. The output of thevariable unit 4 is transmitted through a drum member 8 to a gear 10forming part of the planetary gear train 6.

The variable unit is in the form of a frictional roller drive gearconsisting of three toroidal discs 12, 14 and 16 between which two setsof rollers 18 are in frictional rolling engagement. The middle toroidaldisc 14 is connected to the drum 8 (with freedom to move slightlyaxially) and is mounted on roller bearings around a stationary sleevemember 20. The outer disc 16 is secured to the central shaft 2, whilethe disc 12 has .a spline connection with the shaft 2 and is urgedaxially towards the disc 16 by oil pressure acting in a cylinder definedby a cylindrical wall on a stationary member 24. The oil pressure in thecylinder produces the necessary reaction between the rollers and thetoroidal discs by which the rollers can transmit a frictional drive fromthe outer discs 12 and 16 to the center disc 14.

The drive ratio of the variable unit 4 is varied by altering the ratioangle of the rollers, that is to say the angle about a tangential tiltaxis which determines the distances from the gear axis at which therollers engage the toroidal discs. The rollers are shown at a ratioangle at which they engage the middle disc 14 at a greater radius thanthe outer discs, so that the variable unit transmits a stepped downdrive.

The rollers are mounted in roller carriages 26 which are pivotallymounted in rockers 28 having radially inwardly extending arms 30 pivotedto a control sleeve 32. These rockers are pivoted by pins 34 tostationary spider arms 35 extending from the sleeve member 20. Byadjusting the angular position of the control sleeve 32, the angularpositions of the rockers about their pins 34 can be adjusted, and thiscontrols the tangential positions of the roller carriages andconsequently the ratio angle of the rollers. The angular position of thecontrol sleeve 32 about the gear axis is controlled by a rod 36 pivotedto a lug 38 on the control sleeve. This form of control is described,-for example, in our British Patent No. 1,133,265. It should beunderstood that the control arrangement for the sleeve 32 is shownpurely diagrammatically in the accompanying drawings and that inpractice it is necessary to provide two lugs 38 on opposite sides of thesleeve 32, with two parallel rods connected respectively to the two lugsso that the forces on the sleeve 32 are balanced. The rod 36 is shownconnected to a piston 42. In practice there may be two rods which areboth controlled by the same piston by being connected to opposite sidesof a bellcrank which rocks under the control of a further link connectedto the piston as described in our Patent No. 1,133,266; alternatively,the two rods pivoted to the lugs on the sleeve may form the piston rodsof two separate pistons 42 both connected appropriately to the hydrauliccontrol circuit so as to be urged in opposite directions.

The piston 42 forms part of a ratio jack 40. The function of the ratiojack will be described later on.

The planetary gear train, which is shown diagrammatically, includes anannular member 44 which carries a number of circumferentially spacedplanetary gears 46 (for example three) meshing with the gear member 10.A tubular member 48 is for-med at one end with internal teeth meshingwith the planetary gears 46, and at the other end it is secured to amember 50 which carries a further set f planetary gears 52. The member50 is in turn connected via a sleeve 54 to the output shaft 9 of thesystem. The planetary gear train is completed by a third set ofplanetary gears 56 which are carried by a member 58 which also carriesan annular gear 60 meshing with the planetary gears 52. The planetarygears 56 mesh with a further annular gear 62 connected to the member 44carrying the planetary gears 46.

A rotary part in the form of a brake drum BH is con neoted to the member44 and has a cooperating braking device 64 controlled by a hydraulicjack '66. This brake is operated to lock the drum BH when thetransmission is required to operate in the second regime, that is to saythe regime in which the transmission provides the higher range ofoverall gear ratios. The brake drum BH is freed when the transmission isoperating in the first regime, during which stage a second rotary partin the form of a brake drum BL is held locked by means of a cooperatingbraking device 68 operated by .a hydraulic jack 70. The

'brake drum BL is formed around a sleeve member including a gear 72meshing internally with the planetary gears 52. This sleeve member alsocarries a further gear 74 meshing with a gear wheel 76 from which apower take-off can be obtained when the vehicle is at rest.

It should be noted that alternative planetary gear arrangements can beused, in place of that shown, to produce the same results.

For convenience the second regime of operation, as it provides thehigher gear ratios, will be referred to as the high regime, and thefirst regime will 'be referred to as the low regime.

It will be seen that when the brake drum BL is locked, while the brakedrum BH is allowed to rotate, the output shaft 9 will rotate at a speedwhich depends firstly upon the speed of the input shaft 2 and secondlyupon the speed of the variable unit output drum 8. The input shaft 2rotates always in a clockwise direction (as viewed from the engine end,i.e., the left-hand end), and the variable unit output drum 8 rotatesalways in an anticlockwise direction. The direction of rotation of thetransmission output shaft 9, however, depends upon the gear ratio of thevariable unit during low regime operation. This is shown particularly byFIG. 8. In this graph the curve 78 represents the output speed of thevariable unit (in relation to the speed of the input shaft 2) and showshow this affects the overall gear ratio of the transmission system asplotted against the horizontal axis. It will be seen that the overallratio with this particular arrangement is zero when the variable unitoutput is at about -2.4 (i.e., 2.4 times the speed of the input shaft).When the variable unit output falls below 2.4 in the low regime, theoverall transmission ratio is positive (i.e., the vehicle is drivenforwards), while variable unit outputs above 2.4 in the low regimeproduce a negative overall transmission ratio (i.e., the vehicle isdriven in reverse). As shown also in this graph, the lowest variableunit output is about .75. When the variable unit reaches this point, thetransmission system is changed into the high regime of operation, andincreases in the variable unit output from this point, moving to theright along the curve 78, increase the overall transmission ratio.

FORWARD DRIVINGLOW REGIME FIG. 2 shows the control system in the statein which it propels the vehicle forwards in the low regime. For thispurpose a selector lever 80 is set in the position shown, i.e., at theletter F on a dial 82. This determines the axial position of a generalcontrol valve 84. By virtue of the position of the valve 84, servo oilis supplied to the jack 70 controlling the braking device 68, so as tooperate the braking device 68 and look the drum BL. Accordingly thesystem operates in the low regime.

Servo oil (shown throughout the drawings with a dotted shading) isdelivered primarily by a pump 86 (see FIG. 1) driven from the inputshaft 2, but is also delivered for some purposes by a pump 88 drivenfrom the output shaft 9. Oil in each case is drawn from a reservoir 90.There are two safety valves 94 (see FIG. 2).

Throughout FIGS. 2 to 6, pipes and chambers containing oil at servopressure are shown with a dotted shading, while pipes and chambers shownwithout any shading are at drain pressure. Pipes and chambers shown witha criss-cross shading are at a control pressure which determines theposition of the ratio jack piston 42 and accordingly the transmissionratio of the variable unit 4.

As indicated in FIGS. 1 and 2, a regime control valve 98 is controlledby a changeover mechanism 100 driving a link 106 connected to the regimecontrol valve via a bellcrank 108. The changeover mechanism includes twooppositely acting changeover devices (of which one is shown in FIG. 7)cooperating respectively with the two drums BH and BL. During low regimeforward driving the drum 'BH rotates in an anticlockwise direction (asshown in FIG. 8) and allows the rod 106 to remain in the position shownin FIG. 2 so as to keep the regime change valve in the low regimeposition.

As the transmission ratio of the system increases, the speed of rotationof the drum BH decreases (see FIG. 8), and the gear ratios of theplanetary gear 6 are so chosen that the speed of the drum BH becomeszero at the point when the variable unit reaches the desired limit ofits ratio change in the downward direction. At this point the system isarranged to change to the high regime of operation. This occursautomatically because after reach ing the point of zero rotation, thebrake drum BH begins to rotate in the opposite direction (i.e.,clockwise) and thus drives the cooperating changeover device so as tomove the rod 106 upwards and thus move the regime control valve into theposition shown in FIG. 3, which is the high regime position. When thishappens, servo pressure is cut olf from the jack 70 controlling thebrake drum BL and is delivered instead to the jack 66 so as to lock thebrake drum BH. The system then operates in the high regime. Theoperation of the changeover devices will be described further on withreference to FIG. 7.

As shown in FIG. 2, servo oil is directed from the general control valve84 to a governor valve 112 via a passageway 114. Servo oil enters anannular chamber 116 in the governor valve and from there flows into apassageway 118 past a land portion 120 on the valve which produces apressure drop, so that the pressure in the passageway 118, which is thecontrol pressure for the ratio jack, is lower than servo pressure. Fromthe passageway 118, control oil passes to the lower end of the ratiojack via pipes 123 and 122. A double-acting ball valve 124 is held bythe control pressure against its left-hand seat.

The control pressure at the lower end of the ratio jack provides thenecessary resistance to the torque reaction from the variable unit. Thatis to say when a drive is being transmitted by the variable unit, thecontrol sleeve 32 tends to be rotated in a clockwise direction by thetorque reaction of the rollers. The force on the control sleeve isresisted by the control pressure in the ratio jack. As the controlpressure increases, which is by virtue of movement of the governor valve112 to the left (i.e., increasing the area for flow from the annularspace 116 to the passageway 118 so as to reduce the pressure drop) theratio jack piston 42 moves upwards and thus moves the roller carriagestangentially so as to decrease the drive ratio of the variable unit. Asthe drive ratio of the variable unit decreases, so the drive ratio ofthe system as a whole increases, as shown in FIG. 9 (note that thisapplies of course only to the low regime of operation).

The governor valve 112 is controlled by a governor 126 (see FIG. 1) viaa bellcrank 128, a link 130, a further bellcrank 132, and a valve rod134. The governor is in a conventional form and includes weights 136which are pivoted to a body 138 and tend to force to the left a block140 by virtue of the centrifugal force of the weights. The force to theleft on the block 140 is resisted by a spring 142 extending between theblock and a collar 146 on an axially slidable rod 144 which iscontrolled by an accelerator pedal 148 pivoted on a pin 149. The body138 of the governor is driven from the input shaft 2, so that the block140 tends to move further to the leftas the engine speed increases. Theactual movement to the left does not depend only upon the engine speedbut also upon the position of the accelerator pedal. An increaseddisplacement of the pedal 148 (i.e., in an anticlockwise direction)moves the collar 146 to the right and therefore increases the resistanceimposed on the gOV- ernor block 140 by the spring 142. In practice whatthis means is that the more the accelerator pedal is pressed, the highermust be the engine speed in order to achieve a given amount of movementof the governor valve such as to increase the control pressure. The rateof the spring 142 may be so designed as to provide a substantiallyconstant torque load on the vehicle engine or a torque varying withspeed to suit the engine characteristics and make most efficient use ofthe fuel consumed by the engine in different driving conditions; it may,for example be of a suitable conical shape.

Control pressure from the pipe 122 is also fed via a double acting ballvalve 150 to a pipe 152 from which the oil enters the cylinder space 154between the toroidal disc 12 and the stationary member 24 to provide thenecessary axial loading by which the driving reaction be tween therollers and the toroidal discs is generated. By this arrangement theaxial loading force is maintained at a constant relationship with thetorque reaction on the control sleeve 32, so that the axial loading isat all times neither unnecessarily great nor too small for the torquebeing transmitted by the variable unit.

FORWARD DRIVINGHIGH REGIME As already mentioned, when the transmissionratio of the system reaches the appropriate point, the changeovermechanism moves under the influence of the brake drum BH (i.e., whenthis drum begins its contra-rotation) so as to move the regime controlvalve 98 into the high regime position in which the brake drum BH isarrested while the drum BL is free to rotate. The flow network at thisstage is shown in FIG. 3. It should be noted in particular that thecontrol pressure is now directed by the regime control valve to a pipeinstead of to the pipe 123 as in low regime operation. This means thatthe ratio jack is urged by control oil in the opposite direction, whichis appropriate as the torque reaction on the control sleeve 32 isreversed. Again an increase in engine speed moving the governor valve112 further to the right results in an increase in the control pressure,but this time an increase in control pressure has the reverse effect onthe variable unit; that is to say, an increase in control pressureincreases the drive ratio of the variable unit. In this regime, asopposed to the low regime, an increase in the drive ratio of thevariable unit produces an increase in the igqverall transmission ratioof the system, as shown in As shown also in FIG. 7, during high regimeoperation the brake drum BL rotates in a clockwise direction (i.e., inthe opposite direction to the normal rotation of the drum BH during lowregime operation). The changeover device cooperating with the drum BL issuch as to displace the regime control valve 98 only when the rotationof the drum BL is anticlockwise.

produces the necessary reverse rotation of the drum BL (i.e.,anticlockwise rotation) which results in the drum BL driving itscooperating changeover device in a direction such as to carry the regimecontrol valve back to the low regime position, whereupon the supply ofservo oil to the jack 66 is discontinued, and servo oil is deliveredinstead to the jack 70 so as to lock the brake drum BL. During furtherdecreases in the transmission ratio of the system, the drum BH rotatesin an anticlockwise direction and thus allows the regime control valveto remain in the low regime position.

REVERSE It will be seen that the selector lever 80 remains in the same Fposition for both low regime and high regime operation for forwardpropulsion of the vehicle. In order to drive the vehicle in reverse, theoperator must move the selector lever 80 to the position shown in FIG.4, that is to say against the letter R on the dial 82. As shown in FIG.4, during reverse movement the brake drum BL remains locked and theregime control valve remains in the low regime position. The generalcontrol valve 84 in this case directs control pressure to the upper endof the ratio jack 40 through the pipe 160 as the torque reaction on theroller carriages tends to move the ratio jack piston upwards. As before,the accelerator pedal position and engine speed determine the positionof the governor valve 112, and this in turn determines the pressure ofcontrol oil delivered to the ratio jack. Again, the higher the enginespeed, the higher will be the control pressure. As opposed to the caseof low-regime forward propulsion, an increase in control pressureresults in an increase in the variable unit output speed, which in thiscase results in an increase in the reverse driving speed of the outputshaft 9, as shown in FIG. 8.

NEUTRAL FIG. shows the control circuit in a state equivalent to theneutral position of a conventional vehicle gear box. For this purposethe selector lever 80 is moved to the N position, in which position thegeneral control valve 84 cuts off any supply of servo oil to the ratiojack. Moreover neither of the jacks 66 and 70 controlling the brakedrums BH and BL is supplied with servo oil. Accordingly no power can betransmitted by the planetary gear train 6, and the engine can idle inthe usual way. The ratio jack, being free from control oil, allows thevariable unit to move to and remain in the position of zero overalltransmission output. The regime control valve is held in the low regimeposition by a piston 198 urged by a spring 199 and bearing on theleft-hand end of the valve, so that the valve is held ready for lowregime operation which commences as soon as the selector lever 80 ismoved to the F position. During high regime operation, servo oil isdirected to the piston 198 through a pipe 200 so as to move the pistonto the left against the action of its spring and thus relieve thechangeover mechanism of the need to act against the resistance of thespring 199.

RATIO LIMITING OF THE VARIABLE UNIT It is desirable to limit the amountby which the variable unit ratio can change in the direction away fromthe regime change point. Going towards the regime change point, theratio cannot change excessively, because the regime changing procedureautomatically limits the ratio change. In the other direction, however,it is desirable to protect the variable unit to ensure that the rollerscannot run off the toroidal surfaces of the torus discs. A ratiolimiting valve 180 provides this protection. When the ratio jack pistonmoves downwards to the desired limit, a lever 176 swings about its leftend pivot 179 (see FIG. 2 or 3) and depresses the valve member of theratio limiting valve 180. Consequently oil at a pressure approachingthat of the servo oil is fed to the governor valve via the pipe 184 anddisplaces the governor valve to the right. This permits oil to flow tothe lower end of the ratio jack via the pipes 186 and 122, while thepassageway 118 is isolated from the annular chamber 116 so as todiscontinue the supply of servo oil to the pipe 160. At the same timethe passageway 118 is made to communicate with a passageway 185, via ahole passing through the valve member (shown in dotted outline), andthis leads to drain. As a result the ratio jack piston is moved upwardsaway from the limiting position. This ratio limiting action occurs bothat the extreme high regime position (i.e., at the right-hand end of thecurve shown in FIG. 8) and also at the extreme reverse driving positionshown at the left-hand end of the curve in FIG. 8. It does not come intooperation during low-regime forward propulsion.

The ratio limiting valve 180 also enables the operator to set thevariable unit at a deliberately low ratio if desired, for example inorder to achieve engine braking of the vehicle. For this purpose theselector lever is moved to the left from the F position as shown in FIG.3. As a result a flange 204 on the connecting rod 192, which is normallyheld by a spring 206 against the end of the connector piece 194, ispulled away from the end of the piece 194 (as shown in dotted outline)and engages an arm 164A of a bellcrank 164 so as to swing the bellcrankabout its pivot 166 in a clockwise direction. This carries downwards theleft-hand end of the lever 176, by pulling down a lever 174 against theaction of the return spring 175, and as a result the ratio limitingvalve is opened by the lever 176 at a lower variable-unit ratio. Inother words, moving the selector lever to the left lowers the limitingratio of the variable unit. The further the lever 80 is moved to theleft, the lower will be the limiting ratio of the variable unit. Theextreme left position of the lever 80 is at the letter FL on the dial82. When the lever is in this position, the transmission ratio of thesystem is at the lowest value which can be achieved in the high regime,that is to say at about 0.33 (as shown in FIG. 8).

This action of the ratio limiting valve can occur only when the systemis operating in the high regime, at which stage the piston 170 in thecylinder 172 is held at its extreme right position by servo oil in thecylinder. When the system is in its low regime state, as shown in FIG.2, the cylinder 172 is open to drain pressure, so that movement of theselector 80 to the left would carry with it the piston 170 and would notresult in downward movement of the link 176. I

POWER TAKE-OFF FIG. 6 shows how a power take-01f can be obtained fromthe gear 76 (FIG. 1) by moving the selector lever 80 to the right-handend of the dial adjacent to the letter P. It will be seen that theregime control valve at this stage is in the low regime position. Thebraking devices 66 and 70 are both disengaged, while the output shaft 9is locked by means of a brake 208 (FIG. 1) engaging within a drum 210 onthe shaft 9. Control oil is directed to the upper end of the ratio jack,as during high regime operation, and the arrangement is generally suchthat an increase in engine speed producing an increase in the controlpressure results in a reduction in the variable unit ratio and in acorresponding increase in the overall ratio of the system.

ALTERNATIVE ARRANGEMENT FOR PROVIDING A CONSTANT TORQUE LOAD ON THEENGINE FIG. 9 shows, in the neutral position, an alternative hydrauliccontrol circuit which replaces the engine governor control with a formof control providing for a constant-torque load on the engineindependently of the engine governor. The circuit in this case includesa passageway 212 communicating with servo oil during both high regimeand low regime operation and leading to a passageway 214 (which is theequivalent of the passageway 118 in the previous example) via anonreturn ball 9 valve 216 and an orifice valve comprising an orificememher 220 which is urged to the right by a spring 222 so as to allowthe passageway 214 to communicate with a drain passageway 224 when thereis no servo oil pressure in the passageway 212. When servo oil passesthrough the orifice member 220, it urges this member to the left againstthe action of the spring 222 so as to cut off the communication with thedrain passageway 224, as shown in the drawing.

The regime control valve 226 in this example differs from the valve 98in the previous example.

During high regime operation a pipe 228 delivery control oil to theupper end of the ratio jack via a pipe 230, an annular space 232 in aratio limiting valve 234, and a pipe 236; a double-acting ball valve 238is held against its right-hand seat. A torque-control valve 240 controlsthe pressure of oil supplied to the upper end of the ratio jack so as tomaintain a constant engine torque. This valve is shown in FIG. 10 andwill be described further on. When the limiting ratio is achieved, thevalve member 235 of the ratio-limiting valve 234 is displaced by thelever 176, as in the previous example, but in this case the operation ofthe ratio-limiting valve differs; its eifect is to interrupt thecommunication between the pipe 230 and space 232, and to allow a pipe241 to communivalve 244 being held against its left-hand seat. Thecontrol pressure in this case is controlled by a second torquecontrolvalve 250 which is similar to the torque-control valve 240. As before,the ratio limiting valve does not come into operation during low regimeforward propulsion of the vehicle but it does serve to limit the ratiochange in the upward direction during reverse propulsion, the operationin this case being similar to that in the high regime operation. Thesupply of control oil during reverse propulsion is via a pipe 251, pastthe ball valve 238 and through the pipes 230 and 236 to the upper end ofthe ratio jack; there is in this case no control of torque. FIG. 10shows diagrammatically how each of the torque control valves 240 and 250is arranged, The valve comprises basically a tandem piston assemblyformed by pistons 252 and 254 which are urged apart b a spring 256, thepiston 252 having a narrow end which slides on a central bore in. thepiston 254. Movement of the piston assembly is controlled by a lever 258which is pivotally connected to the piston 254 by a pin 262. The lever258 is itself mounted on a pivot 260. i The pipe in which the pressureis to be controlled to achieve constant torque is shown as the pipe 264.From this pipe a connecting pipe 266 leads to a blow-off cylinder 268via a restricted orifice 270.The cylinder 268 contains the piston 252and has a blow-otf port 272 through which oil can escape into a pipe 274leading to I drain. Blow-oflt is controlled by the right-hand end of thejack piston 42 in the case of the torque control valve .240 (for highregime operation), but corresponds to downward movement of the torquecontrol valve 250 (for low regime operation). It will be seen that thefurther the lever 258 moves in a clockwise direction, the higher must bethe oil pressure in the blow-off chamber 268 before blow-off into theport 272 occurs. The rate of the spring 256 is carefully chosen so thatthis arrangement gives rise to a constant-torque load on the engine.

On opposite sides of the orifice 270 in the pipe 266 there are laterallyextending pipe sections 278 and 280 serving as cylinders containingpistons 282 and 284 bearing on a lever 286 which is pivoted about anadjustable fulcrum 287. The pipe 280 has a blow-off port 288 leading todrain via a pipe 290. Blow-off is controlled by the piston 284. The oilpressure in the blow-off cylinder 268 depends upon the amount ofblow-off through the pipe 280. Accordingly the value of constant torquemaintained can be adjusted by varying the position of the fulcrum 287along the lever 286. Displacing the fulcrum to the right results in anincrease in the value of constant torque at which the engine willoperate, and vice versa. This enables the operator to reduce the torquedemanded from the engine when the engine becomes weaker through wear orfor any other reason.

As a further alternative the torque control system of FIG. 1 may bemodified by arranging, in effect, that the position of the collar 146bearing on the governor spring 142 responds directly to the torque ofthe engine, rather than to the position of the accelerator pedal. Forthis purpose a measure of the torque output of the engine may beobtained from the center gear member 13 of the planetary step-up gear 5,which would in this case not be rigidly secured against rotation butwould be re strained against rotation by an appropriate springarrangement, so that the member 13 is angularly deflected during use toan extent directly dependent upon the engine torque; the collar would,.for example, be connected to a radially extending lever on the gearmember 13 so as to move closer to the governor body as the engine,torque increases.

The engine of the vehicle may be tow started, that is to say by towingthe vehicle, for example if the engine self-starter is out of action. Toachieve this, the control lever is placed in the N position, and afterthe vehicle has been accelerated to a sufiicient speed by towing, thelever is moved to the F position, whereupon the engine is driven so asto start. Forward driving then carries on as before.

FIG. 7 shows one of the changeover devices, namely that associated withthe brake drum BL, as viewed from the input end of the transmission. Asshown by the long arrow 302, the normal direction of rotation of thedrum is clockwise. This occurs while the system is in the high regime ofoperation, the drum BI-l being locked.

The regime control valve is itself controlled by the link 106, aspreviously described. As shown in FIG. 7, the link 106 is pivotallyconnected to a link 300 via a bellcrank 301, the link 300 beingconnected to a toggle member 304 pivotally mounted on a pin 306. Acompression spring .308 is shown urging the lower end of the togglemember against a stop 311 0. The toggle member remains in this positionuntil it is rotated clockwise past the dead center position (in whichthe center-line of the spring passes through the pivot 306), whereuponthe spring 308' rapidly rotates the toggle member further in a clockwisedirection and holds it against a stop 312. A chain-dotted outline showsthe toggle member in this alternative position which corresponds to thelow-regime position in that the link 106 is then in its upper position.

Movement of the toggle member is achieved as follows. So long as thedrum BL is rotating clockwise, nothing happens to the toggle member.However, when the drum BL comes to a stop and then begins itscontra-rotation (indicated by the shorter arrow), a pivoted abutment 314engages the adjacent end of the finger 316 and rotates the finger in aclockwise direction about a pivot pin 318. Movement of the finger isresisted by a strong tension spring 320 which has one end 322 anchoredto a stationary 1 1 frame 324 and has its other end hooked through ahole 325 in a latch 326 which is pivotally connected to the finger by apin 328. As the finger 316 is carried clockwise by the abutment 314, thelatch touches the toggle member, but can ride past the toggle member (toapproximately the position shown in chain-dotted outline) because thespring 320 yields to permit it to do so. As soon as theabutment 314passes the finger 316, thus permitting the finger to return under theaction of the spring 320, the spring 320 snaps the finger and latch backto their former position (shown in solid outline); during this returnmovement the latch rotates the toggle member in a clockwise directionpast the toggle dead-center position, and the movement of the togglemember is then completed under the action of the toggle spring 308. As aresult the link 300 moves to the left and depressed the link 106 whichin turn moves the regime control member to the lowregime position inwhich the brake is applied to lock the drum BL.

Subsequent movement of the toggle member back to its former position isachieved by means of a second changeover device consisting of a secondassembly which is in efifect a mirror image of the finger 316 latch 326,spring 320 and abutment 314. This second assembly is axially spaced fromthe first assembly to enable the second abutment to be secured to thedrum BH, while the second finger equivalent to the finger 316 may bepivotally mounted on an extension of the pin 318. The toggle member isnaturally of sufiicient thickness to lie in the paths of both latches.

It should be noted that the abutment 314 is pivoted to the drum BL by apin 330. Pivotal movement is limited in both directions by a pin 332 onthe drum which passes through a curved slot 334 in the abutment. Thisallows the abutment to swing in a clockwise direction under the actionof centrifugal force acting on the heavier end of the abutment (i.e.,the end extending further from the pivot pin 330). This swinging carriesinwards a raised portion of the abutment. It is this raised portion thatis capable of engaging the finger 316; the remainder of the abutment isarranged to miss the finger. Accordingly, when the drum BL is rotatingat some speed, this arrangement keeps the raised portion 336 out of theway so as not to click over the end of the finger at each revolution. Asthe drum BL slows down to a stop (on approaching the regime changepoint), the abutment is returned to its normal position (shown in solidoutline) by a light tension spring 337 so as to be ready to engage thefinger when it begins its contra-rotation. While the drum "is rotatingslowly in a clockwise direction, the abutment clicks pass the finger,being moved inwards by the finger through a cam action.

In the above description, only one abutment 314' has been mentioned. Inpractice there may be two or more output speed of the system as theengme speed increases,

similar abutments evenly spaced around the drum to reduce the maximumpossible angle of contra-rotation which can occur before the toggle isoperated. v

I claim: c 1. A variable speed transmission system comprising a variableratio transmission unit of which the drive ratio is steplessly variable,a transmission input member driving said variable ratio transmissionunit, a transmission output member and a planetary gear train, saidtransmission output member being driven by said variable ratiotransmission'unit via said planetary gear train characterized in thatthere is further provided two rotary parts of the planetary gear trainwhich normally rotate in opposite directions, two brakes and two regimechange-over devices, each of said brakes and each of said regimechange-over devices being associated with one of said rotary parts, aregime control member which is connected to the said regime change-overdevices and which is operable thereby between a first and a secondposition, means for actuating said brakes alternately so as to lock saidrotary parts alternately to provide two regimes of operation of saidtransmission system, a fluid pressure-actuated means for varying thedrive ratio of said variable ratio transmission unit, first and secondfluid inlet ports in said regime control member, first and second fluidoutlet ports associated with said first fluid inlet port, said firstfluid inlet port communicating with said fluid pressure-actuated meansvia said first fluid outlet port to provide one mode of operation ofsaid fluid pressure-actuated means when said regime control member is insaid first position and communicating .with said fluid pressure-actuatedmeans via said second fluid outlet port to provide a reversed mode ofoperation of said fluid pressure-actuated means when said regime controlmember is in said second position, and third and fourth fluid outletports associated with said second fluid inlet port, said second fluidinlet port communicating with said third fluid outlet port when saidregime control member is in said first position and communicating withsaid fourth fluid outlet port when f said regime control member is insaid second position going contra rotation and to unlock the brakeassociated with the other rotary part, each rotary part being arrangedso that as the system approaches the change-over point between the tworegimes, the rotary part then rotating in its normal direction ofrotation will slow down and then commence to rotate in the contradirection.

2. A transmission system according to claim 1, for use as a vehicletransmission, in which the first regime of operation, which is the lowregime for the vehicle, in-

cludes a zero output speed which occurs at an intermediate setting ofthe variable unit ratio, so that changes from this ratio in onedirection provides a low-gear forward drive, while changes in the otherdirection provide a reverse drive for the vehicle.

3. A transmission system according to claim '2 in which the variableunit is a frictional roller drive gear comprising a plurality of rollersand at least two torus discs wherein said rollers drive frictionallybetween said torus discs.

4. A transmission system according to claim 3, in which there isprovided a control sleeve which controls the ratio angle of saidrollers, said control sleeve being itself controlled by said fluidpressure-actuated means for which the pressure is varied in response tothe engine speed and in response to the vehicle accelerator setting orengine torque,'so that the variable unit tends to increase with but onthe other hand tends to decrease the output speed, that is to sayproduce a lower over-all transmission ratio,

' in response to 'an increase in the engine torque or in the fuel supplyto the engine as determined by the acceleraj tor setting.

5. A transmission system according to claim 4 in which there is furtherprovided a constant torque valve system 'and a blow-off arrangementwhich limit the pressure of fluid applied to said fluidpressure-actuated means in response to the position of said controlsleeve.

References Cited ARTHUR T. McKEON, Primary Examiner US. Cl. X .R. 74865

